Process for producing shaped oriented polyester articles having a metallic luster



1960 D. s. ADAMS ETAL 2,948,583

' PROCESS FOR PRODUCING SHAPED ORIENTED POLYESTER v ARTICLES HAVING A METALLIC LUSTER Filed March 4, 1958 2 Sheets-Sheet 1 INVENTORS DUSTIN S. ADAMS ROBERT S. PRENGLE ALBERT ERNST BY M ATTORNEY Aug. 9, 1960 s ADAMS EI'AI. 2,948,583

D. PROCESS FOR PRODUCING SHAPED ORIENTED POLYESTER ARTICLES HAVING A METALLIC LUSTER Filed March 4, 1958 2 Sheets-Sheet 2 x- I 29 YPI 6.0

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-x- 0am mu HAS z METALLIC LUSTER E z -e- 0am YARN ms CONVENTIONAL CLEAN wnuumcs so 40 so a0 ammo TEMPERATURE c BY Q ATTORNEY United Sta es Pat Patented Aug. 9, 1950 PROCESS FOR PRODUCING SHAPED ORIENTED POLYESTER ARTICLES HAVING A METALLIC LUSTER Filed Mar. 4, 1958, Ser. No. 719,124

- 19 Claims. CI. 18-54) This invention relatesto synthetic polyester films and filaments. More particularly, it relates to a process for producing polyethylene terephthalate films, ribbons and filaments which have a metallic luster.

Recently, films having a metallic luster have come into great demand. Metallized yarns and films have been prepared by laminating thin metal foils to a clear polymer base or by vacuum depositing a metal on the polymer base. These films and filaments, however, are not proving entirely satisfactory for many commercial-purposes. Since they are comprised of dissimilar materials, process- 2 V producing the lustrous articles comprises drawing an article of the aforementioned polymeric ester, which has an initial birefringence of not more than'tltll, at its natural draw ratio at a temperature below 80 C. to at least 5.0 times its original length at a drawing speed of at least 0.75 yard per minute and less than 50 yards per minute. Preferably, a polyethylene terephthalate article is shaped so that the initial birefringence is below 0.01, the drawing temperature is between 25 C. and 75 C., and drawing from 5.0 to 7.0 times the original length is accomplished at a drawing speed of from 2.to 17 yards ing baths and the like must be selected so that they will not damage the material. In addition, surface abrasion and adhesion problems, that is, separation of the metal coating from the polymer base, have been experienced. Also, the elasticity of the polymer base can not be fully utilized because the elasticity of the metal coating is a limiting feature. Furthermore, the manufacturing proc esses and the equipment required to perform these processes are complicated and expensive.

High molecular weight condensation polymers, particularly the polyesters of the type described in Whinfield and Dickson, US. Patent No. 2,465,319 have been utilized in preparing films and filaments. Processes for laminating metal foils to a polyester'base as well as processes for producing filaments having variations in denier, i.e., with short, thick sections alongthe fiber axis, have been described. However, polyester filaments of uniform denier which have a metallic luster have heretofore been unknown. Markwood, 'U .S. Patent No. 2,352,- 725 does describe a process for producing a pearlescent effect in polyamide filaments. This effectis somewhat similar to that obtained by the process of the present invention; however, the teaching of the patent is not an adequate guide to selection of processing conditions to produce continuously a lustrous polyester filament. Furthermore, the process described by Markwood, which is limited to drawing at rates under 1.5 inches per second, is entirely unacceptable from a commercial standpoint. It is, therefore, an object of this invention to provide films, ribbons and filaments which have a metallic luster from a single material. Another object is to provide a commercially acceptable process for drawing polyethylene terephthalate films, ribbons and filaments'whereby a metallic luster appearance is imparted to the drawn articles. A further object is to provide a process for preparing polyester filaments which have uniform denier, high tenacity, and superior surface characteristics. Other objects will be apparent from the following description.

The objects of this invention are achieved by providing a highly oriented and uniformly drawn shaped article comprised of a cold-drawn highly polymeric ester of a dicarboxylic acid and a dihydric alcohol, said ester being. capable of being formed into filaments which when cold-drawnshow by'characteristic X-ray pattern molecular orientation along the fiber axis, elongated voids along the fiber axis, a metallic luster, and a densityof from 0.6 to 1.3 grams per cubic centimeter. The processfor per minute.

The invention will be more readily understood by re? ferring to the following detailed description and the accompanying drawings- In the description the terms films, ribbons and filaments are meant to include and will be used interchangeably throughoutthe specification with the term yarn. Flat ribbons, round monofilaments, filament bundles, warp sheets, as well as ribbons and'monofilaments of other regular and irregular cross-sectional configuration, are included within the scope of this invention.

By the phrase natural draw ratio is meant a draw ratio at which a certain degree of permanent, nonreversible extension, which is just sufiicient to change it from its undrawn state to'a uniformly drawn'and highly oriented state without straining the polymeric material so as to introduce surface cracks or failure, is given to the polymeric material. In general, when any material is drawn in the conventional sense used in processing synthetic fibers one or both of two things happen. There can be plastic flow and there can be orientation of the material. The plastic flow method of drawing is used to elongate a polymeric material 10, 2O oreven times its original length. However, in the plastic-flowprocess only slight orientation of the material occurs. Plastic flow drawing isnormally carried out eitherat high temperatures or in the presence of plasticizers, or both. There is no natural draw ratio for plastic flow elongaeon; When a synthetic polymer is not in a plastic flowable condition it will, under normal conditions, tend to draw atits natural draw ratio and in the process become highly oriented. If, for example, an undrawnfilament can be drawn to five times its original length to produce a highly oriented, uniformly drawn material, it is not possible, in general, to .draw it completely at either four or six times its original length under the same conditions. If one attempts to draw to six times, the filament will break. If one chooses a lower value, for example, four times, one will find that some sections of the yarn will draw at the natural draw ratio while other sections will not draw at all.

Drawing speed is another critical term in the process which must be defined. The present process employs a necking-down step in which the yarn diameter is sharply reduced within a short axial length. Immediately preceding the neck the yarn is essentially unoriented and beyond the neck the yarn is highly oriented. By drawing speed" it is meant the rate at which fullydrawn material'is caused to move'relative to -the drawing neck. For purposes of convenience the drawing speed is measured in yards per minute. r V The temperature at which this drawingtakes place is also highly critical. In citing the drawing temperature, the temperature of the yarn just prior to the point where it starts to draw is referred to. At this point the temperature is controlled by the temperature of the surroundings. If the yarn is wrapped on a pin or caused to contact a flat surface for some distance, it will approach thermal equilibrium with the-surface it contacts. If the yarn is keptfor severalminutes in contact with air;heat to-a certain temperature, equilibrium will also be established.

At the drawing point or' neck, the yarn will, of course, be much hotter. It has not been possible to measure this temperature accurately, but it is estimated that the yarn temperature approaches the melting point of the polymer.

In the drawings,

Figure 1 is a schematic drawing-showing a preferred embodiment of apparatus for the continuous drawing process of this invention;

Figure 2 is a schematic drawing in section showin suitable apparatus for drawing small lengths of yarn; and

Figure 3 is a graph showing the relationship between the drawing temperature of a polyethylene terephthalate yarn and the natural draw ratio at certain drawing'speeds.

Referring to Figure 1 of the drawing, reference numeral 1 represents an essentially unoriented yarn which is withdrawn from a source not shown and passed around feed rollers 2 and '3. The axes of the feed rollers are positioned at a slight angle to each other to cause a separation of the yarn helices and an advancement of the 'yarn'along the rollers- The yarn is arranged with a 'sufficient number of turns about the feed rollers to prevent "slippage. Yam 1 must have a birefringence of not more than 0.01 and is preferably at room temperature. The yarn is passed from the feed rollers over or adjacent to a heated tube 4 whereby it is heated to a temperature of not'more than 80 C., preferably from 25 C. to 75 C. The yarn is then passed to drawing rollers 5 and 6 which are operated at a speed sufiiciently greater than the feeding rollers to draw the yarn from 5.0 to 7.0 times its original length. The speed of the drawing rollers is regulated so that the drawing takes place at the natural draw ratio. The axes of the drawing rollers are positioned at a slight angle in the same manner as described for the feed rollers. The yarn is arranged with a sufficient number of turns about the set of rollers to prevent slippage. From the drawing rollers, the yarn is passed through traversing device 7 and then wound up on bobbin 8 which "may be rotated'by means of the surface of drive roller 9. The yarn draws at its natural draw ratio with a sharp necklocated within a stable narrow zone near heated tube 4.

Referring to the apparatus shown in Figure 2, reference numeral 10 represents an insulated box in which electrical heating means 12 and temperature control "means 13 are positioned, A sample of yarn 14 is placed in'the box, heated, and withdrawn through opening 11. "This apparatus and its use will :be further described in "discussing the graph of Figure 3.

'The natural draw ratio of polyester filaments is primarily controlled by the drawing temperature and the "'drawing speed. Referring to Figure 3, it will be noted that a particular drawing temperature there will be a corresponding natural draw ratio at which the undrawn polyester material will preferentially elongate to the highly oriented, uniformly drawn, lustrous state. Therefore, when the drawing temperature is selected according -to'the process of this invention, the draw ratio is determined-to conform to this condition. Alternatively, it is f possible to select the drawing ratio Within the range stated {for this invention and to control the temperature gradient through which the material passes during the drawing step according to the limits previously set forth. At a specific "point in the temperature gradient zone Where the tempera- -"ture'corresponds to the selected draw ratio, the drawpoint will stabilize.

'The draw ratio is also affected by the drawing speed. As-the'drawingspeed is'increased and the filament is heldata given temperature, the natural draw ratio Will "increase. Figure 3 illustrates this point. For example, fitatemperature of 60 C., the natural draw ratio increases from about 5.15 to 6.45 as the drawing. speed is creased from 1.2 yards per minute to 17 yards per minute. The data used in preparing Figure 3 were obtained using *the apparatus shown in'Figure 2. An insulated asbestoscharacteristic of overstrainedpolymeric materials.

concrete board box 10 was made with a small opening 11, one inch by one-half inch, on one side. Electrical heating means 12 and temperature control means 13 were placed inside the box. Forced air circulation was used to maintain a constant, uniform temperature throughout the box. A sample of undrawnpolyethylene terephthalate yarn 14 having a birefringence of 0.0003 was attached to a fixture 15 on the insideof the box opposite the small opening and creased at the fixture. The box was maintained at the desired temperature for ten minutes, during which time the yarn reached thermal equilibrium with this temperature. The loose end of the yarn was then attached to a windup roller 16 and the yarn pulled from the box at a constant speed. As soon as the slack was removed from the yarn, thematerialstarted to neck-draw at the crease. The neck of the drawn yarn moved toward the windup roll at'a speed governed by the windup speed and the natural draw ratio. The yarn selected its own natural drawratio as determined by the temperature and the windup speed. .The drawing operation was stopped when the draw point emerged from the box.

A short section of the undrawn yarn near the fixed end was marked'and its length measured prior to'drawing. The ratio,

Length after drawing Length before .drawing gave the natural draw ratio R. Knowing the windup speed, S, the drawing speed, A, was then calculated using the formula Using'a range of temperatures and windup speeds, the plots for Figure 3 were made. For other combinations of variables, if the draw ratio and draw speed are known, the drawing temperature can readilybe determined by the foregoing procedure. Because only a few of the many combinations of drawing speeds, temperatures and resulting natural draw ratios which may be used in practicing this invention have been shown in the figure, it is not intended that the scope of the invention-be limited by the data shown therein.

The temperature gradient in the yarn can be provided by various means other than the heated tube 4 shown in Figure 1. A hot surface which the yarn is caused to contact, having heating units distributed below the Surface so that the yarn temperature increases along the path, may be used. Alternatively, the yarn may be passed between two heated elements. In addition, other thermal barriers such as a liquid or gas interface can be employed. as can other radiant heating-apparatus.

Under the conditions which have been previously described, the filament will draw at its natural draw ratio in a very short distance. During the drawing step the polymeric material becomes interspersed with a'large number of tiny, elongated voids. These voids are gener-' ated within the boundaries of the ribbon or filament and are in no way to be confused with a milky appearance due to surface cracks or internal, brittle failure which is The drawn ribbon has a very thin, clear skin. By virtue of the tiny, elongated voids and the very thin, clear skin, filaments produced by this process have a metallic luster. However, the products of the present invention are superior to and entirely different from laminated or coated structures containing, for example, metal foil or deposited metal film. While laminated structures reflect only light which strikes the planeof the'metal surface, the lustrous product of this invention reflects and refracts light which strikes the filament at any angle. It has also previously been pointed out that the physical properties of the materials of this invention are not limited by the elasticity of a metal or by'a bond between the'filamentnn'd laminate,*orby'thephemical stability of a metal or Comparison of laminated and deposited metal, (alumiestates coarser materials can be used to prepare products as have beenconventionally prepared with the prior art metallized structures. The finer forms, however, have many new applications in the area of decorative fabrics, for example, lam fabrics which heretofore were produced only with relatively heavy yarn to give the metallic appearance. These new materials may be used in'fabrics now employing conventional polyester fibers for making articles such as blouses, shirts, sheer knitted goods, tricot fabrics, and the like. I

6 ventional fibers would be used. For example, the density of the materialis extremely low due tothe presence of theincluded voids. Commercial polyethylene terephthalate fibers have a density of about 1.4. The present materials are produced with a density range of from 0.6 to 1.3 with a density of from 0.6 to 1.0 being preferred. Of course, if the density is below 1.0, the yarn will float on water. Because of the low density, a greater length of yarn of a given cross-sectional area may be obtained from When the products of the present invention are ob tained in physical dimensions equivalent to prior art laminated structures, the new products exhibit outstanding advantages in strength and elasticity. Table 1 shows the superior tenacity and elongation of the products of the present invention. In interpreting the data of Table 1, it is necessary to recognize that the figures in 'theelongation column must be compared not only on the basis of the film elongation but also on the basis of the elongation limit of the metal. For example, a metal laminated film elongated to, 5% more than its original length. would become defective as well as unsightly due to the metal breaking even though the film backing would remain intact. The products of the present invention, however, can be stretched to at least 10% greater than their original length without any damage.

TABLE 1 num) lustrous ribbons with metallic luster'polyester ribbon [1/64 inch;

Initial Modulus are. mer? Tenacity Elonga- (gJdeon Density (percent) (g./ce.)

Material Denier nier Metal-laminated polyester filmh- (a) Metal Limit Polyester film with vacuum-deposited metal coating (a) Metal LimiL- Metallic luster polyester ribbon.

Stretched in two directions and heat-sat at elevated temperature.

TABLE 2 Comparison of physical properties at other fibers with products of this invention Elongation (percent) Initial Modulus (gJdenier) Tenacity l Material (gJdenier) Metallic luster yarn Polyester fiber Nylon yarn Cellulose acetate fll ents Metallized polyester ribbon.

a given weight of polymer.

In addition to the low density, these drawn structures have an extremely low dyeability. When they are woven into a composite fabric with other conventional fibers, the fabric can be dyed by conventional processes, and under such conditions the portion of the fabric prepared from the metallic-lusteryarn will not accept the dye, Thus, striking dyed efiects can be obtained in different colors in the same fabric with a pattern of metallic-luster yarn which'retains its original color.

The drawn structures of this invention also have a higher fiber stillness than conventionally drawn fibers. In view of this fact, they are particularly well suited for embroidery work, gold braid, rugs, and fiberfill. They may also be used as a reinforcing agent in resin sheets or slabs. Their greater stillness provides excellent reinforcingproperties in addition to the highly decorative effect. Because of the presence of the tiny voids or air spaces, these materials have a high covering power: and high opacity as well as low heat transfer. For these reasonsthey are suitable for use as batting for quilts, con1 forters, sleeping bags, and other insulating structures.

The metallic luster imparted to the products prepared the metallic luster.

processing and use of the finished material, that is washing, 'drying, fulling operations, and the like do not alfect However, designsmay be embossed on the yarns, fabrics and films prepared from these inaterials by'using high, localized pressure.

The drawing process described herein is readily controllable. However, only by operating within the limits stated can the new and valuable products of this invention be obtained. The combination of limits specified are in themselves unusual, and differ greatly from those noted as p in the. art for drawing polyesters to produce clear filaments. In particular, the drawing temperatures are lower and the draw ratios preferred in the present process are,

in general, 50% to 100% higher than those used in prior nature of the limits previously mentioned are further illustrated but not intendedto be limited by the following examples. 1

I 7 EXAMPLE I 1 A ribbon of polyethylene terephthalate was spun by a conventional melt spinning technique to give a ribbon 1.20 mm. wide and 0.15 mm. thick having a birefringence in the as-spun state of 0.0003. This ribbon was drawn using apparatus similar to that shownin Figure l. The relative surface speeds of the feed rollers and drawing rollers were such that the material was drawn 6.0 times its original length; A inch stainless-steel tube, heated to a dull red heat, was held approximately inch away from the 7 thread line. The heated tube set up a temperature gradiminute. The draw ratio and drawing speed of thisdrawing" operation indicated that thetemp erature of the yarn.

just prior to the draw point was C. Under the con ditions set forth, it was possible to draw the ribbon continuously. The resulting ribbon had a metallic luster and upon. examination proved to'be full of elongated A round monofilament of polyethylene terephth alate was melt spun with a diameter of0.24 mm. .The initial birefringence of this filament was 0.0025. A portion of this monofilament was placed in the previously described box shown in Figure 2 with one end of the filament attached to theinterior wall of the box. The'yarn was allowed to remain in the box at a temperature of 65 C. until thermal equilibrium had been established. Oneend of the undrawn filament was then wound upon a drawing roller at a speed of 12.5 yards per minute. The yarn drew within the box from the fixed end at a draw ratio of 6.8x. The resulting yarn monofilament had a final diameter of 0.08 mm. The drawn monofilament had a bright metallic luster and had a density of slightly below 0.62 g./cm. was wound up on the roller corresponds to a drawing speed of 14.7 yards per minute.)

EXAMPLE III was drawn to 5.7 times its original length. The resulting drawn material was a ribbon 0.80 mm. wide and 0.04 mm.

thick with a bright metallic luster throughout its length,

the ribbon having a large number of elongated internal voids. The ribbon had afinal density of about 0.7 g./om.

I EXAMPLE IV Example HI was repeated except that the undrawn ribbon was heated to 70 C. and was drawn at a speed of 1.2 yards per minute to give a ribbon with a continuous metallic luster. The density of the ribbon was less than 0.80 g./cm. The draw ratio in this test was 5.05 X

EXAMPLE V Another sample of the undrawn ribbon described in Example I11 was conditioned in a room at a temperature of 25 C. The yarn was then slowly drawn on an lnstron tensile tester at a draw speed of 0.75 yard .per minute, at a draw ratio of 5 .2 The resulting ribbonwas'0.80 mm. wide and 0.035 thick, and had a continuousluster. It was not possible to draw the ribbon at lower speeds and get a continuous luster. At lower speeds, for example 0.36 yard per minute, the resulting drawn material drew at a lower draw ratio, 5.0 times its original length, and did not have a continuous luster. At even lower speeds, the draw ratio decreased and the luster entirely absent. (This example illustrates the lowest drawing speed for practicing the process of this invention.)

EXAMPLE v1 A sample of the undrawn ribbon described in Example III was conditioned in the box .at 68 C. and was then drawn at a draw speed of 45 yards per minute. Under these conditions, the natural draw ratio was 6.8.x. The resulting product was a ribbon 0.90 wide and 0.05 mm. thick, having a continuous luster. This material had a density of 0.62 to 0.65 g. cm. It was possible although difiicult to draw ribbon under these conditions at this speed to produce a continuous filament. Breakageo-f the filament, however, occurred occasionally. When the same experimentwas repeated at the same temperature but at a speed of 49 yards per minute, .it was not-possible (The speed at which this-monofilament' to maintain a steady drawing. The yarn broke at every trial.

, EXAMPLE VII Thisexample shows that an upper limit for the temperature of the process'of this invention exists. In Example III it was shown that it was possibleto drawapolyethylene terephthalate ribbon at a temperature of 75 C. and at a draw ratio of 5.7x. A sample of the same undrawn ribbon was conditioned in the box shown in Figure 2at a temperature of C. An attempt was made to draw theribbon at the same speed, that is, 16.9 yards per minute. However, at this temperature the draw ratio dropped from 5 .7 x to 4.6x and the yarn instead of having, ametallic luster was clear, having the appearance of conventionally."drawnpolyethylene terephthalate; The density of this-clear ribbon'was measured and found to be 1.379 which is normal for conventionally drawnp'olyethylene terephthalate. There were no voids in the ribbon. It was apparent that under these conditions it was not possible to operate the process of this invention. Referring to Figure 3, it is shown that upon increasing or decreasing the speed a lustrous product was not obtained at this temperature. Thus, at 80 C., only a clear, conventionally drawn ribbon rather than a lustrous-ribbon can be obtained.

EXAMPLE VIII Two flat n'bbons of polyethylene terephthalate were melt-spun. One-of. the ribbons had a denier of 205 and was 0.40 mm. .wide and 0.03 mm. thick. The birefringence of this ribbonwas- 0.01. This higher birefringence 2. The box was held at ajternperature of 25 C. After reaching thermal equilibrium, the ribbon was drawn at a speed of 14.85 yards per minute, under which conditions the yarn had a natural draw ratio of 5.2x. The resulting ribbon was-0.-25 mm. wide and 0.005 mm. thick and had a density of 1.293 g. /cm. The ribbon was faintly lustrous but drawing was difficult under the conditions stated. r The other sample of ribbon was melt-spun and wound up at a slightly higher rate, giving an undrawn ribbon having a denier of and a birefringence of 0.011. The ribbon was placed in the conditioning box which was held at 25 C. and then drawn at a speed of 15.5 yards per minute. The natural draw ratio was 4.4x The resulting ribbon'was'clear and had a density of 1.379 g./cm. It was not possible toobtain la metallicluster product in any polyethylene terephthalate 'having abirefringence greater than 0.01.

EXAMPLE IX Molten polyethylene terephthalate was spun through a 30-hole :spinneret .ofwhich-eaeh hole was 0.009 inch in diameter to give a multifilament yarn. Birefringence prior to drawing was about 0.001. The yarn bundle was passed over a heated plate and then drawn. Drawing temperature was between 68 C. and 75 C. The draw ratio was 6.0x and the drawn yarn was wound up at approximately 8 yards per minute. The final product was a multifilament yarn of 30 filaments, each filament having a denier of 6. The yarn had a bright, silvery metallic luster.

EXAMPLE X.

An essentially amorphous, unoriented polyethylene terephthalate'filrn was drawn in a'longitudinal direction between a group of slow and fast rolls. In determining the initial birefringence of the film, the procedure included directing abeam of polarized light upon edges of the film perpendicularto' both the longitudinal direction and transverse direction of thefilm. The birefringence so measured wasfound to 'beless than 0.01 in'both direct-ions. The filmwas fed over and undera series of five slow The higher windu'p speed induced a small rolls, and then. for adistance of abrolltj fQQ l qfi l' being threaded through the group of live fast rolls. The

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1 Machine Direction.

Transverse Direction. p 7. 1 V

The foregoing examples illustrate theoperable ranges for the process ofthis invention, the criticality-of the limits of operability, and the desirability of the, preferred ranges previously set forth. s It has been showninthe. examples that at temperatures of 80.? C...and above it is not possible to draw substantially amorphous. polyethylene terephthalatematerial and :obtain ametallic lusr. ter. 7 At such temperatures the fiber or ribbon draws to a. clear product such as describedin the prior It has been shown that extremely low draw speeds, i.e., below 0.75 yard per minute, will not givefa lustrous'rnaterial and that speeds below50 yardsper minutemust be used.

It has also been shown that the. material tolbe drawn must have an initial birefringence of not-more than f0 0l in order to obtain the product of this invention.

By controlling the birefringencet mperature and. drawing speed, it is possible to obtain :in aLsingIeQoperation a filament exhibiting boththefcharacteristics ofconventionally drawn yarn and yarnjhaving aImetallic-luster. By the proper choice of drawi g geometry, the filament can be forced to travel a non-.unifprmnpathf so j that in one section of the path the yarn is'pre-orienteithat is oriented so that the birefringence is. above.0.0l and when drawn will give a clear ribbon. Inftheoth er portion of the'path, the yarn isQnotp re-oriented and when drawn gives a metallic luster, As aresultj a ribbon having alternatingclear andlustrons sections can be prepared. A process for preparing such ribbons is described in the copending. application of Dustin S. Adams Serial'No. 719,144, filed concurrentlyherewith; Y

As previously stated, the process of this invention is operable only at temperatures below 80f C., temperatures in the range of 25 C. to 75 (3. being preferred. At very low temperatures thetension necessary to draw the polyethylene terephthalate increases greatly and breakage of the material *in' either'the drawn or undrawn state may occur. It is possible, however, to practice this invention at temperatures as lowas lQf Q or lower; In all cases the drawing temperature must be higher; than that oithe undrawn fiber prior toenteringfthe drawzone; The process'of'this invention may be utilized to pro duce materials having metallic luster which may or may not contain dyes or pigmentation, provided the inclusion of the pigments or dyes does not increase the birefringence of the undrawn yarn above 0.01 or act as a plasticizer. While undyed yarns of polyethylene terephthalate give a silvery appearance when drawn by the gamesprocess of this invention, goldappearing yams. copperf tones, reds, greens, and blues can be obtained by dyeing the polymer or yam with suitable colors. Suitable dyes for application to the melt-spun undrawn ribbon or filamerit include 1-amino-2-bromo-4-hydroxyanthraquinone and l-(p-ethylolamino)-4,5-dihydroxy 8 nitroanthraquinone. Of -course, it is also possible to color the products of this invention by including a dyestuif such as those described in US. Patent No. 2,571,319 in the melt prior to spinning. Small amounts, up to 0.5% by weight of the polymer, of opaque white pigment such as titanium dioxide and barium sulfate can be added. In addition, other opaque colored pigments such as cadmium sulfide, lamp black, and the like, may be used. The opaque solid pigments give a more subdued metallic luster. The small amount of foreign material, pigment. or dye, does not interfere with the drawing process.

It has been indicated that the'cold-drawing process of this invention takes place with the formation of an abrupt neck, at which point the diameter of the drawn material is sharply reduced. Neck-drawing is, of course, a wellknown phenomenon, and the neck-drawing of polyethylene terephthalate films has been described in prior art processes. However, it is believed that the neckdrawing process as practiced in the present invention is significantly different from that of the prior art. The

profile of the filament being drawn at the draw point discussed in theprior art is much less abrupt than that found in the present invention. The neck produced in the present invention is extremely sharp, i.e., the shoulder of the neck forms an abrupt angle greater than 44 with the fiber axis, which indicates that the present process employs anew type of drawing with a very high rate of shear being produced in a very short distance. In .the clear drawing process, the neck angle is only about 35. While it is not intended that theoretical considerations or hypotheses should limit the scope of this invention, it

is apparent that the rate of shear encountered in the present process is somuch greater than that encountered in conventional cold-drawing processes that an entirely new phenomenon is observed. It is quite possible that the high shear rate is responsible for the generation of the many tiny voids which givethe products of this in vention their unique and desirable metallic luster.

{Following the drawing step of this invention, it is possibleand usually desirable tolhea't-stabilize the drawn yarn 'by subjecting it to heat in the temperature range C.200 C. or higher, thus causing it to shrink controll-ably from 0 to 35% of its original length. This gives a product of improved appearanceand dimensional stability;

In practicing this invention, polyesters prepared as described in the aforementioned Whinfield and Dickson Patent U.S. 2,465,319 are preferably used. The polymers may contain small'amounts of impurities and reaction byproducts which generally appear in continuous polymerization processes without adversely affecting the proc-, ess' of the present invention. Polyester filaments comprised of modified polyethylene terephthalate, i.e., polyethylene terephthalate copolymcrs containing residues of other dicarboxylic acids such as isophthalic acid, phthalic acid, naphthalic acid, and bibenzoic acid, or other glycols may be drawn to a metallic luster.

In the normal operation of this process, the filaments will be spun, wound up ,on'bobbins andstored for a period of time before being drawn to a metallic luster. it has been found that the process is most readily controllable when the filamentary material to be drawn has been allowed to age at room temperature for periods iron 24 to 48 hours; however, material aged from 1 to 2 hours at from 60 C. to C. performs quite satisfactorily. While it is not intended that the scope of this invention be limited in any way by speculative theories, it is hypothesized that, during the aging period, a certain degree of amorphous association develops in the polymer which permits the generation of greater shear during the drawing process. When a multiplicity of filaments are being drawn simultaneously, the addition of an anti-static agent is frequently used. It has not been noted that ambient conditions of relative humidtiy have any significant effect on the drawing process or on the qualities of the polyester product.

Many advantages over the prior art produces and processes accrue from the present invention. A simple process is provided which is easily controllable whereby attractive decorative materials, yarns, films, and the like having a metallic luster are obtained. This process not only gives a superior product with respect to physical properties but also eliminates the elaborate and expensive steps which have heretofore been required in preparing metallic-appearing yarns. The present process gives an added advantage in that it can be adapted to produce both round and irregular yarns as well as flat ribbons. In addition, single films or ribbons, yarn bundles or warp sheets may be drawn by this process. A further advantage lies in the fact that the low denier multifilament and monofilament fibers while having a high metallic luster can be handled in the same manner as conventional polyester yarns and fibers. A still further advantage lies in the fact that the yarns of this invention have increased strength, improved extensibility, are substantially chemically inert to conventional dyeing, bleaching, scouring, and other textile processing treatments to which many laminated metallic yarns cannot be subjected. Still another advantage lies in the unique and desirable properties of these yarns due to their low density, void-containing structure, and high covering power.

The shaped articles of this invention have a wide variety of end uses. The articles, in film form, may be used as base materials for the preparation of magnetic recording tapes and for fabricating a variety of other types of tapes such as pressure-sensitive adhesive tapes, adhesive tapes, binding tapes, surgical tapes, and tear tapes for opening cartons and packages. Due to their unique void-containing structure, the shaped articles are particularly desirable for use in electrical applications in the form of pressure-sensitive tapes, slot insulations for motors, as a dielectric in condensers, and as an insulating wrapping for wires and piping.

The lustrous filaments and ribbons of this invention may be woven or knitted into fabrics of all types. They may be used in preparing attractive drapery materials, clothing, upholstering, rugs, and the like,

Included among the many other products which may be preparedfrom the shaped articles of this invention are window shades, tracing cloth, ticker tape, heat-shrinkable films and filaments, typewriter ribbons, and reflective thermal insulators.

Since the products of this invention have the property of becoming clear in areas when pressure is applied, for example, by drawing, stamping or typing on them, films so treated may be used as a negative in preparing a number of copies of any desired subject matter on photosensitive paper. Other end uses for the products prepared as described herein Will be apparent to those skilled in the art.

It will be apparent that many widely different embodiments of this invention may be made Without departing from the spirit and scope thereof and, therefore, it is not intended to be limited except as indicated in the appended claims.

We claim:

1. The process of producing a shaped oriented article comprised of a highly polymeric ester of a dicarboxylic acid and a dihydric alcohol, said ester being capable of being formed into filaments which when cold drawn show by characteristic X-ray pattern molecular orientation along the fiber axis, which comprises drawing a shaped article of said ester which has a birefringence of not more than 0.01 at its natural draw ratio at a temperature below 80 C. to at least 5.0 times its original length at a drawing speed of at least 0.75 yard per minute and less than 50 yards per minute ,whereby a continuous metallic luster is imparted to said article.

2.. The process of claim 1 in which said article is in the form of a filament.

3. The process of claim 2 wherein said filament is drawn from. 5 .0 to 7.0 times its original length.

4. The process of claim 1 wherein said temperature is between 25 C. and C.

5. The process of claim 1 wherein said drawing speed is between 2 and 17 yards per minute. 7

-6. The process of claim 1 wherein said polymeric ester is polyethylene terephthalate. V

-7. The process of claim 1 wherein the birefringence of. said shaped article is below 0.003.

8. The process of claim 1 wherein a plurality of filaments are drawn simultaneously.

9. The process of claim 1 wherein said article is in the form of a film.

10. The process of producing a textile yarn which comprises spinning a filament of a molten, highly polymeric ester of a dicarboxylic acid and a dihydric alcohol, said ester being capable of being formed into filaments which when cold drawn show by characteristic X-ray pattern molecular orientation along the fiber axis under conditions whereby the filament has an as-spun birefringence of not more than 0.01, aging the filament for a period of at least one hour, and drawing the filament at its natural draw ratio to more than 5.0 times its original length at a drawing speed of at least 0.75 yard per minute and less than 50 yards per minute at a temperature of less than C. whereby a metallic luster is imparted to said yarn and said yarn is highly oriented and uniformly drawn.

:llJThe processof claim 10 wherein said filament is drawn from 5.0 to 7.0 times its original length.

(1 2. The process of claim 10 wherein said temperature is between 25 C. and 75 C.

13. The process of claim 10 wherein said drawing speed is between 2 and 17 yards per minute.

14. The process of claim -10 wherein said polymeric ester is polyethylene terephthalate.-

'15. The process of claim 10 wherein the birefringence of said filament is below 0.003.

16. The process of claim 10 wherein a plurality of filaments are drawn simultaneously.

17. The process of claim 16 in which said filaments are drawn in the form of a warp sheet.

18. The process of claim 16- in which said filaments are in the form of a yarn bundle.

19. The method of producing a textile yarn which comprises heating a polyethylene terephthalate filament which has a birefringence not greater than 0.01 to a temperature between 25 C. and 75 C. and drawing said heated filament at its natural draw ratio at a drawing speed between 2 and 17 yards per minute to from 5.0 to 7.0 times its original length whereby said filament is fully drawn and a metallic luster is imparted tosaid filament.

References Cited in the file of this patent UNITED STATES PATENTS 2,465,3'19 Whinfield et a1 Mar. 22, 1949 2,497,376 Swallow et a1 Feb. 14, 1950 2,734,794 Calton Feb. 14. 1956 UNITED STATES-PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2 948 583 Y August 9, 1960 Dustin S, t Adams et a1,

' It Its-hereby certified that error appears in theprinted specification of the above *numbereipatent requiring correction end' that the said Letters Patent should read as corrected below.

Column 3 line 73, for "creased" read increased column 5 Table l heading to the third column after "(g./deni insert a closing parenthesis; same column Table 2 under the heading "Elongation (percent-)'" line 3 thereof for "14.22" read 14-22 Signed and sealed this 25th day of April 1961.

SEAL) ttest:

ERNEST w. SWIDER DAVID L. LADD Attesting Oflicer Commissioner of Patents 

10. THE PROCESS OF PRODUCING A TEXTILE YARN WHICH COMPRISES SPINNING A FILAMENT OF A MOLTEN, HIGHLY POLYMERIC ESTER OF A DICARBOXYLIC ACID AND A DIHYDRIC ALCOHOL, SAID ESTER BEING CAPABLE OF BEING FORMED INTO FILAMENTS WHICH WHEN COLD DRAWN SHOW BY CHARACTERISTIC X-RAY PATTERN MOLECULAR ORIENTATION ALONG THE FIBER AXIS UNDER CONDITIONS WHEREBY THE FILAMENT HAS AN AS-SPUN BIREFRINGENCE OF NOT MORE THAN 0.01, AGING THE FILAMENT FOR A PERIOD OF AT LEAST ONE HOUR, AND DRAWING THE FILAMENT AT ITS NATURAL DRAW RATIO TO MORE THAN 5.0 TIMES ITS ORIGINAL LENGTH AT A DRAWING SPEED OF AT LEAST 0.75 YARD PER MINUTE AND LESS THAN 50 YARDS PER MINUTE AT A TEMPERATURE OF LESS THAN 80*C. WHEREBY A METALLIC LUSTER IS IMPARTED TO SAID YARN AND SAID YARN IS HIGHLY ORIENTED AND UNIFORMLY DRAWN. 